Optical modulator

Abstract

An optical modulator includes a substrate, an optical waveguide, a control electrode applying a high frequency signal in order to modulate light waves propagating through the optical waveguide, and a relay substrate provided with a relay line to transfer the high frequency signal to the control electrode. The control electrode and the relay line together have a coplanar line structure inclusive of at least electrical connection portions of both the control electrode and the relay line. The control electrode includes an electrical connection portion and a routing portion positioned between the electrical connection portion and an active portion applying an electrical field to the optical waveguide. The routing portion has a coplanar line structure. A distance between ground electrodes sandwiching a signal electrode in the electrical connection portion of the control electrode is substantially equal to a distance between ground electrodes sandwiching a signal electrode of the routing portion.

What is claimed is: 
     
       1. An optical modulator comprising:
 a substrate having an electro-optical effect; 
 an optical waveguide formed on the substrate; 
 a control electrode formed on the substrate and applying a high frequency signal in order to modulate light waves propagating through the optical waveguide; and 
 a relay substrate provided with a relay line in order to transfer the high frequency signal to the control electrode, 
 wherein the control electrode and the relay line together have a coplanar line structure inclusive of at least electrical connection portions of both the control electrode and the relay line, 
 the control electrode comprises an electrical connection portion of the control electrode, and a routing portion positioned between the electrical connection portion of the control electrode and an active portion applying an electrical field to the optical waveguide, 
 the routing portion has a coplanar line structure, and 
 a distance G 2  between ground electrodes sandwiching a signal electrode in the electrical connection portion of the control electrode is substantially equal to a distance G 1  between ground electrodes sandwiching a signal electrode of the routing portion. 
 
     
     
       2. The optical modulator according to  claim 1 ,
 wherein a distance G 3  between ground lines sandwiching a signal line in the electrical connection portion of the relay line is substantially equal to the distance G 2  between the ground electrodes sandwiching the signal electrode in the electrical connection portion of the control electrode. 
 
     
     
       3. The optical modulator according to  claim 2 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a length L of the pad portion is set to a tenth or less of a wavelength of the high frequency signal. 
 
     
     
       4. The optical modulator according to  claim 3 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a width S 2  of the pad portion is set to a tenth or less of the wavelength of the high frequency signal. 
 
     
     
       5. The optical modulator according to  claim 4 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       6. The optical modulator according to  claim 3 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       7. The optical modulator according to  claim 2 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a width S 2  of the pad portion is set to a tenth or less of the wavelength of the high frequency signal. 
 
     
     
       8. The optical modulator according to  claim 7 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       9. The optical modulator according to  claim 2 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       10. The optical modulator according to  claim 1 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a length L of the pad portion is set to a tenth or less of a wavelength of the high frequency signal. 
 
     
     
       11. The optical modulator according to  claim 10 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a width S 2  of the pad portion is set to a tenth or less of the wavelength of the high frequency signal. 
 
     
     
       12. The optical modulator according to  claim 11 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       13. The optical modulator according to  claim 10 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       14. The optical modulator according to  claim 1 ,
 wherein the signal electrode in the electrical connection portion of the control electrode is electrically connected from the relay line and comprises a pad portion having a largest width and a tapered portion which continues from the pad portion to the routing portion, and 
 a width S 2  of the pad portion is set to a tenth or less of the wavelength of the high frequency signal. 
 
     
     
       15. The optical modulator according to  claim 14 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material. 
 
     
     
       16. The optical modulator according to  claim 1 ,
 wherein a material of the substrate having an electro-optical effect is lithium niobate or a polymer-based material.